Peremennye Zvezdy (Variable Stars) 33, No. 2, 2013
Received 13 February; accepted 22 February.
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|We present two transiting exoplanet candidates in Cygnus discovered during a small photometric survey performed at the Kourovka Astronomical Observatory of Ural Federal University in the summer of 2012. The MASTER-1 b candidate (host star 2MASS 20260213+5006032, ) has a period of 0847, transit depth of 0015, and transit duration of 16. The MASTER-2 b candidate (host star 2MASS 20341625+5015427, ) has a period of 0983, transit depth of 0017, and transit duration of 17. We believe that these transit-like signals might be caused by Hot Jupiters. Observations, data reduction, transit search tools, and detected candidates are described. Follow-up photometric and spectroscopic observations are needed to clarify the nature of the candidates.|
The instrument consists of a pair of 40 cm Hamilton catadioptric telescopes with the focal length of 100 cm, installed on the same equatorial mount and equipped with two Peltier-cooled Apogee Alta U16M CCD cameras. The image scale is 1.85 /px. The observations can be performed simultaneously in two filters (the Johnson-Cousins system) or in two different polarization planes.
At the time of our summer observations, we obtained frames only in the filter, with 50 exposure times, because only one of the CCD cameras worked properly. However, additional observations in December, 2012 were made in the and filters. For photometric calibration, we used dark-current frames obtained before each observational night and flat-field frames obtained on the morning twilight sky after every observational night. All observations were carried out in automatic mode.
Photometric data were obtained for 21500 stars with accuracy from 0006 to 006 for stars from 100 to 160, respectively. To convert the instrumental magnitudes to the standard system, we used Johnson and SDSS magnitudes from the UCAC4 catalogue (Zacharias et al. 2012) and equations from Jordi et al. (2006) to derive Johnson magnitudes.
To search for transit-like signals, we selected about 5000 stars with the standard deviation of magnitudes for the entire series of observations less than 002, i.e. for which it is possible to detect a transit of a Hot Jupiter with a depth of about 001. Searching for periods was performed with the BLS method (Box-fitting Least Squares, Kovács et al. 2002) using the VARTOOLS package (Hartman et al. 2008). Periods with a high S/N ratio on the periodogram were used for plotting phase curves. Transit fitting was also performed in the VARTOOLS package. As a preliminary result, we discovered two stars with strong transit-like signals.
According to the 2MASS catalogue (Skrutskie et al. 2006),
magnitudes of the host star 2MASS 20260213+5006032 are
. From our
observations in two filters made in December, 2012,
. Following Pickles (1998), the color indices
were used to estimate the approximate spectral type of the star
without accounting for interstellar redening. The formal spectral
type of the host star is G0-M8. The proper motion of the star is
mas/yr (Roeser et
al. 2010). The upper limit to the distance is 2300 pc from the
proper motion, as it follows from the equation:
Transit fitting using the Mandel-Agol transit model (Mandel & Agol 2002) was performed with the VARTOOLS package. Initial parameter values were determined based on the results from the BLS search method. For fitting, we used a quadratic limb-darkening law, varied the ephemeris ( and ), ratio of planet radius to host star radius (), ratio of semi-major axis to host star radius (), and inclination (). Eccentricity and argument of periastron were set to 0 and not varied. As the result, we have: , , , , .
The magnitudes of the host star 2MASS 20341625+5015427 are , , and . According to our observations, and . The formal spectral type of the host star is G8-K5. We found no data on the proper motion of the host star.
Transit fitting was performed in the same way as for the first candidate: , , , , .
Assuming that the host stars belong to the main sequence and have solar-like sizes, the candidates' radii and semi-major axes correspond to the Hot Jupiter type (like the known exoplanets WASP-18 b, WASP-19 b, and WASP-43 b). To verify the spectral types and luminosity classes of the host stars, follow-up spectroscopic observations are needed.
Acknowledgements: We would like to thank Ekaterina Avvakumova and Anna Punanova (Kourovka Astronomical Observatory) for their valuable remarks. This work was partly supported by the Federal Task Program "Research and Operations on Priority Directions of Development of the Science and Technology Complex of Russia for 2007-2013" (contract 14.518.11.7064), by the Russian Foundation for Basic Research grant 12-02-31095, and by a grant in the form of a subsidy from Ministry of Education of the Russian Federation (Agreement No. 8415 of August 27, 2012).
This research made use of Aladin (Bonnarel et al. 2000).
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